The invention relates to a piezoelectric actuator, for example for actuating a mechanical component, such as a valve or the like, comprising a piezoelectric element, which is provided with a multi-layer structure of piezoelectric layers with internal electrodes disposed between them and with external electrodes making electrical contact with the internal electrodes on alternate sides.
It is generally known that a piezoelectric element operating according to the piezoelectric effect can be constructed out of a material with a suitable crystalline structure. The application of an external electrical voltage causes a mechanical reaction of the piezoelectric element which, depending on the crystalline structure and the region to which the electrical voltage is applied, produces a compression or tension in a predictable direction.
The piezoelectric actuators mentioned above are frequently used in valve positioning. Among other things, their stroke capacity for actuating a valve tappet, for example, is relatively small and thermal expansion of the ceramic of the piezoelectric element can lead to a drift in the position of the valve tappet when the piezoelectric element is not triggered. Also, contact with the active parts of the piezoelectric actuator is difficult.
It is an object of the present invention to provide a piezoelectric actuator, which does not suffer from the above-described disadvantages.
The piezoelectric actuator described at the beginning, which can be used, for example, to actuate a mechanical component, advantageously has a piezoelectric element that generates a tensile or compressive force acting on an actuation element, which is provided with a multi-layer structure of piezoelectric layers with internal electrodes disposed between them and with external electrodes contacting the internal electrodes on alternate sides of the piezoelectric element.
In this connection, it is particularly advantageous that the external electrical connections for the lateral contacting are affixed to an inactive end region in the layer structure and the end region has a core with favorable heat conductivity. As a result, the external contacting of the piezoelectric actuator in inactive end regions that are not affected by tensile or compressive forces, which contacting must be reliably produced, can be easily combined with favorable heat dissipation in order to avoid the disadvantages described at the beginning.
In one advantageous embodiment, the inactive end region has a relatively thin, electrically insulating cover layer on the layer structure. The cover layer is provided with a heat-conducting core which in turn has electrically insulating ceramic layers affixed to its sides. The connection between the external electrodes and the external electrical connections can thereby be produced in the ceramic layers. Preferably this can be achieved by means of a solder layer which is applied to the respective ceramic layer in the vicinity of the external electrodes. In another likewise very advantageous embodiment, the inactive end region comprises an electrically insulating ceramic part in which the connection between the external electrodes and the external electrical connections can be produced at the sides. In this embodiment. a heat-conducting core is embedded in the ceramic layer. In a particularly preferable way, in the plane of the layers, the core has a round contour and is consequently disk-shaped on the whole.
These and other features of preferred improvements of the invention ensue from the claims, the specification, and the drawings, wherein the individual features can be realized singly or multiply in the form of sub-combinations in the various embodiments of the invention and in other areas and can represent advantageous and intrinsically patentable embodiments which are claimed herein.